The present invention relates to poly(N-phenyl urethanes), to methods of preparing same from poly(N-phenyl iminocarbonates), and to poly(N-substituted iminocarbonates) in general, and to methods of preparing same.
Unsubstituted polyurethanes carry a moderately reactive --NH-- group in their backbone that severely limits the polymer's thermal stability. The thermal stability of polyurethanes can be increased by the replacement of the NH proton by an alkyl or aromatic substituent. In particular, fully aromatic polyurethanes, such as, for instance, poly(Bisphenol A N-phenyl urethane) would be a mechanically strong material stable at very high temperatures.
Poly(N-substituted urethanes) have been prepared as disclosed in Mukaiyama et al., J. Orq. Chem., 27, 3337 (1962), Fujisawa et al., Bull. Chem. Soc. Japan, 37(6), 793 (1964) and Macromolecular Syntheses, Vol. 4 (W. J. Bailey, ed., John Wiley and Sons 1972) pp. 105-108. However, these polymers have been limited to ethylene N-substituted urethanes prepared by the ring-opening polymerization of cyclic ethylene N-substituted iminocarbonates. This method is unsuitable for the preparation of fully aromatic polymers containing commercially desirable diphenolic monomers that are incapable of forming cyclic iminocarbonates.
Poly(N-substituted urethanes) have also been prepared by the condensation polymerization of dichloroformates with substituted diamines as disclosed in U.S. Pat. No. 3,373,139 to Morgan: ##STR1## Although a variety of poly(N-alkyl urethanes) have been prepared in this way, poly(N-phenyl urethanes) are not as readily accessible because of the high cost and limited availability of the required N-phenyl diamines. Thus, an alternative method for the synthesis of fully aromatic polyurethanes would be of considerable practical utility.
With respect to the poly(N-phenyl iminocarbonates) from which the poly(N-phenyl urethanes) are prepared co-pending patent application Ser. No. 219,290, now U.S. Pat. No. 4,980,449 describes polyiminocarbonates generally useful as degradable polymers, having unsubstituted imino nitrogens. The disclosure of polyiminocarbonates and methods of synthesizing polyiminocarbonates in said U.S. patent application Ser. No. 219,290 is hereby incorporated herein by reference thereto.
A drawback to the polyiminocarbonates of U.S. patent application Ser. No. 219,290 is that the imino group is heat sensitive with thermal decomposition temperatures (T.sub.d) close to the glass transition temperatures (T.sub.g) of the polymer. Most of the polyiminocarbonates of U.S. patent application Ser. No. 219,290 lack sufficient thermal stability to be compression molded and must be formed to the desired shape without using heat to soften or melt the polymer.